This invention relates to a screw type pump and more particularly to such a pump which is used for conveying waste water or the like by means of a substantially vertical screw which is mounted for rotation within a fixed pipe that surrounds the screw and defines a conveying channel, with the pipe having an inlet opening at the lower end thereof and a discharge opening at the upper end thereof.
Vertical screw pumps have an advantage over bucket wheels and inclined screw pumps in that the expense of providing a separately designed complicated structure is eliminated. That is, the vertical screw pump is in the form of a completely constructed unit which only requires that it be suspended into the waste water channel or tank from which the liquid is to be conveyed. In addition, vertical screw pumps reach their maximum capacity at a speed of from 300 to 500 rpm and at the same time do not require a costly gearbox. While centrifugal pumps operate at still higher speeds, there is the inherent danger that the activated sludge flocs will be broken down. To achieve a useful efficiency, inclined screw pumps must have a gradient of approximately 40.degree. and a shaft diameter which is at least 50% of the screw diameter. With vertical screw pumps, on the other hand, the shaft can be extremely thin since the shaft is not subjected to transverse forces. This is particularly advantageous since it increases the discharge capacity. Also, with a vertical screw pump, the lower shaft bearing can be eliminated so that the inlet flow is not impeded.